Martin Meredith

Thanks for this info Mike. Aladin (and Vizier and Simbad) really are wonderful resources and we are so lucky to have access to all this literature. Good luck with your VV trawl. It is definitely a good approach in terms of spotting treasures like this. I am more haphazard but if something looks interesting on the charts I sometimes strike lucky. I never look at Aladin first though -- that really would be cheating! Tonight is another clear one -- so tiring 🙂 I still have another 20 or so Berkeley OCs to observe but this means dragging the scope out to the back of the house and it is a bit of a wind tunnel on a breezy day like today, so it is likely to be more Pegasus for me tonight... Martin

Here's a very fine and maybe under-appreciated group from the VV catalogue: VV84. This was a chance encounter from last night. I took one look at this and started searching for alternative designations. Surely this must also be an Arp? a Hickson? VV84 strongly resembles Hickson 79 -- Seyfert's Sextet (or is it Septet?). But no. Here's a wide field (well, 0.4 degrees!) shot which shows just how compact this group is. And here is a closeup of the group, oriented N [EDIT: Looks like I mislabelled a galaxy here: PGC 70012 is actually NGC 7433 (mag 14.0 Sbc). It appears PGC 70112 is the same galaxy, but it is odd that it has different listed magnitude] I couldn't find much information online. One of the few references http://articles.adsabs.harvard.edu/pdf/1989ApJ...345..176L regards VV84 as a triple system but there are more than 3 galaxies involved to my eyes, with 6 having reported distances around 350 MLys. I read that the main elliptical, NGC 7436, contains a supermassive black hole, and one report suggests that it contains little or no dark matter https://arxiv.org/pdf/0906.4448.pdf. The pair NGC 7435/7436a are partially overlapping and have been used to study light absorption of background by foreground galaxies https://arxiv.org/pdf/astro-ph/0007361.pdf. There are other interesting groups in the wider shot, including the 3 edge-ons (one bright, 2 faint) to the lower right. Its an intriguing side-question to consider why VV 84 didn't make it into the Hickson catalogue, or given an Arp designation. After all, some Hickson groups are also Arps and VVs, some VVs are Arps, etc. Hickson's paper is well worth a read was it goes a little into the chronology of compact group discovery and of course lays out his selection criteria. http://articles.adsabs.harvard.edu/pdf/1982ApJ...255..382H In this case it might be that the bright edge on to the lower right (UGC 12274) is regarded as part of the VV84 group -- it has a similar distance estimate -- and maybe then the group as a whole fails the compactness criterion. Opinions? cheers Martin

Very interesting link that, Chris. I was thinking of having a go until I spotted the surface brightness ... It shows there is still much to be discovered by amateurs. Martin

Excellent shots of these great targets. Funnily enough I was also looking at them the night before last. There is an awful lot going on in Hickson 92 and the longer you look the more of the wispy tails become visible. You're getting great detail for 2 minutes total exposure. Martin

This is a group I came across by accident last night in Lacerta. There are two VVs here. VV 1935 is classified as PC = 'pair of coalescence'. It is hard to see which are the galaxies here due to the field stars, but I see two small oval candidates (aligned 10 o'clock and 2 o'clock), each seeming to emerge from behind an accompanying star... VV 1936, also classified as NGC 7240, is M-type, meaning M51-type with one satellite. The M51 galaxy is quite clear but what isn't obvious is whether the satellite is the block just above it, or the slight nodule on what looks like a very thin spiral arm at the S of the galaxy. The other galaxy in this shot is the mag 15.4 SBb-type IC 1441 (it looks elliptical here). I spent quite some time on this pair, not just to look for the details, but because they are part of a very interesting wider field (which also helps put the apparent size of the VVs into content): This is a part of the sky (near the border with Cygnus and Pegasus) where the stars are still quite dense which I think adds to the interest. NGC 2742 is the bright galaxy just above the centre. This is a mag 14.0 elliptical. It is more interesting than many ellipticals that I've observed with a very extensive halo. There are some lovely edge-on galaxies here too (hence the framing). The one to the right is UGC 11963, a mag 14.9 S0-a type with a dense core and flying saucer shape. Looking somewhat similar, at 8 o'clock is PGC 68466, a mag 15.6 Sab-type. I'm not sure if this group has a designation but does seem to be regarded as a group. The earliest reference I can find to it is a 1920 paper by Pease http://articles.adsabs.harvard.edu/pdf/1920ApJ....51..276P which talks about 20 members. Distance estimate are in the range 250-320 MLyrs so it is possible that some of these are physically-linked. cheers Martin

Thanks everyone for your replies. I do set up each session but I also have mains power nearby and most of my usage nowadays is just outside the house, so mains power would work. I bought a regulated power supply from Maplin some time ago for this purpose but have never used it -- now is the time to get this set up. But I'd also like to have a portable supply for the odd times when I visit dark sites. The Celestron PowerTank seems like a great option -- certainly much lighter than my current car starter battery (which admittedly has served me very well for 6 years of very regular use and also serves to inflate footballs...). Great setup Magnus by the way! Its about time I used the saddle mount on my az-eq6.... Jon, yes, I read your other thread about low current issues with your Star Adventurer (I also have that mount and the batteries last ages so no issues so far). cheers Martin

Thanks -- I often wonder what he thinks when I get the rig out. In winter he probably things I'm mad... (he doesn't join me in all weathers).

I've been using a car starter battery since 2014 to power my Skywatcher Az-eq6 GT mount but it is starting to drain about 90 minutes into each session, so its time to look for a replacement. Things have moved on since 2014 and I'm wondering what others are using to power this (or similar) mounts? For instance, I have a LiZone 60000maH power bank that I use for laptop charging. Is this useable, or going to be sufficiently beefy for this mount? I have absolutely no idea about power supplies so please treat me as an utter beginner here! Martin

Callum, I hope you don't mind if others post their setups on this thread? I'd certainly be interested to see what everyone's rig is like. Assuming you don't, here is my complete setup (from last night). I keep fit by manhandling it out and in most clear nights (usually minus one of the 5kg weights 😉 ) It hasn't changed much for some years now. This is my usual observing location where I get a reasonable view from ESE to SW. The wooden terrace is a bit springy which isn't ideal but as I tend to observe from just inside the door (esp in winter), it is only a problem when the dog is wandering around. Skywatcher Quattro Newtonian 8", carbon fibre tube, f4 (800mm focal length). Its mainly stock, but I've applied some flocking inside and to the rear of the primary and changed the secondary adjustment screws for Bob's Knobs, not that it made a vast difference. This is occasionally collimated with a CatsEye autocollimator (hotspot symbol applied to primary). Skywatcher Az-EQ6 mount, only ever used in alt-az mode. Starlight Xpress USB filter wheel, 9 slots (Clear, R, G, B, Ha, OIII, SII, spectral grating and a piece of flocking taped over for darks) Starlight Xpress Lodestar X2 mono camera Car starter battery 2 USB cables to the laptop I've got a cheap digital thermometer hanging off the scope that I use to record the temperature when I'm taking or applying darks, and a Rigel Kwik Finder, plus a bahtinov mask and a light shield that I use on non-windy nights. I'm probably old school in that I do everything from the hand controller. No plate-solving or software controlled gotos yet. A longer cable from the hand controller would be my preferred upgrade as then I can do everything from just inside the almost closed door when its gets chilly. As it is, I get up between objects to type in the RA/Dec for the more obscure DSOs. Since 2014 I have only ever used LodestarLive (now StarlightLive), latterly with Jocular, and now that Jocular supports the Lodestar and SX filter wheel natively, I just use Jocular. I always have a copy of my deep maps open on screen (PDFs) and am constantly flicking between the image building up and the charts to see what is going on... I used to use SkySafari during 2-star alignment when I couldn't identify the relevant stars (embarrassing) but since upgrading laptop I'm using Stellarium for the same purpose. cheers Martin

Fascinating to hear about these plumes in NGC 7674. They sound like a real challenge. I'm trying to ID the PGC galaxy but I have it down as PGC 214960 (mag 17.4). Here's a shot of mine from long ago when I was still using my colour Lodestar. Some dust bunnies here, and colourful hot pixels. Also, a rather sleek flat galaxy in the upper right (must be PGC 71461).

More or less simultaneously (we are one hour ahead, at 23.30) I was also looking at Arp 86, initially in mono, then with some colour added in. The left pair of shots are 3 minutes total in 15s subs. Top right is 11 minutes (2 mins in each of RGB and 5 in L), but viewed in mono. Bottom right is 8m 15s shown in colour. There is a little more coming out in the longer inverted exposure -- the background is smoother so a few more details of the fainter parts are visible. The colour version doesn't add very much but more detail of the companion galaxy is visible in the colour shot, presumably due to the reduced transmissibility (the companion is pretty bright in luminosity). Like yours, these are also using hyper stretch.My stars are noticeably squarer close up!

Beautiful image and description. Having checked out the amazing JPL image I can make out the start of the twin tails in your shot. There's a nice challenge to see how much of those tails one can pull out. I'd like to visit this one in colour. The Lodestar has quite good near-IR sensitivity apparently. I do have a shot of this from a few years ago -- quite poor in comparison with yours (also taken in September I see). It is much smaller than it appears in your zoomed image. You're getting some remarkable detail in 7s subs. cheers Martin

I'm on a Mac so can't really help there I'm afraid. I'm guessing you downloaded from here? https://ffmpeg.zeranoe.com/builds/ On the Mac at least you end up with a command line tool (ie not a GUI-based application). Martin

I use ffmpeg for all my conversions involving video/sound (though I've not used it for Astro purposes). Its very complete, robust and free. https://ffmpeg.org Cheers Martin

Interesting pairing as you say. Cases like this where one is somewhat further way than the other give a real feeling of depth, especially as they appear to have a similar actual size. Thanks for the detailed description. When I saw the Arp number (46) at first I thought we were in true ring galaxy territory but I am out by 100... Martin

Not so grubby! Plenty of resolved stars and the hint of a lot more in the halo. What kind of stretch function are you using? I find log works well with globulars in particular. Martin

Thanks Greg -- there's quite a bit of structure in the ring itself I can see in your shot. I wonder if the double stars are the result of the aligner rather than tracking (or perhaps a consequence of the aligner not doing the right thing with a mistracked sub)? Alignment generally needs to correct for rotation and translation differences between subs but not for scale differences, and this case looks to me like it is trying to account for the latter too. Does AltairCapture allow you to specify what kind of alignment constraints to apply? Do you typically keep your individual fits files? It would be interesting to have a go at aligning these subs. cheers Martin

Thanks for the contribution Mike. The Abell planetaries certainly are challenging and for EEA observing timescales probably have to be treated like faint/dwarf galaxies, with deep exposures in monochrome as you've done here. Smaller pixels won't help (and will make things harder in my opinion) for these fainter objects as there will be fewer photons per pixel in any given time, so you'd end up binning anyway. For brighter PNs the reverse will be the case and a smaller pixel sensor (everything else being equal) ought to help a lot, assuming the seeing is up to it. Narrowband is worth a try always, assuming it is easy to slot the filter into the light path in a 'what if' kind of way. This is something I hope to do more of. I haven't done a lot of narrowband recently but I remember having a great time a few years back using StarlightLive to combine luminosity and H-alpha for some of the brighter galaxies. Martin

Thanks, Bill, Mike & Callum. Believe me, these nights are rare here and I made the mistake of not extending the session far into the early hours because I didn't want to be like a kid in sweetshop, rather thinking of saving some for other nights. A bad decision.... In general August has been quite poor here too -- maybe 4 or 5 clear nights.

Thanks Jeremy. I've been using StarlightLive (SLL) for most of my EEA life since it was released in 2014 I think, but more recently I've been using Jocular, some EEA software I'm developing. Originally I used SLL to 'feed' subs Ito Jocular ie as a capture engine, but in the most recent version of Jocular I've implemented native support for the Lodestar, so it all happens from Jocular. I've also managed to get the SX electronic filter wheel controlled natively, so the whole LRGB capture can be done in a single button press, which means I can concentrate on observing the image building up. SLL was the only way up to now (I think) of doing this kind of multispectral capture in a live setting -- definitely a pioneering piece of software. Martin

Here's a live LRGB shot of the Lagoon Nebula from a few days ago taken with my 8" f4 reflector and Lodestar X2 mono guide camera plus Baader filters (just under 6 minutes -- details on the shot). This was a rare night of marvellous seeing. [Ignore the temperature reading -- it was nearer 20C; and I'm guessing that the SQM was around 19.5 with the moon still up] The Lagoon Nebula (M8) has a little of everything. Apart from the great flowing mass of the nebula itself, it houses several of Barnard's dark nebulae, an open cluster (NGC 6530), a nebulosity within the nebula (the Hourglass), as well as 9 Sgr, one of the most luminous stars known (actually, a binary with a period of 9 years); the luminosity is 100s of thousands times larger than our own sun. 9 Sgr and its neighbour are mainly responsible for lighting up the nebula. Some of these components are indicated on the single 15s sub below (yes, this is bright, even at under 20 degrees of altitude). The hourglass is the pink bowtie near the centre of the upper part of the cluster; rotated by 90 degrees the hourglass shape becomes clearer. This cluster is being ionised by a multiple star 'Trapezium-like' system known as Herschel 36 (the bright object to the right of the hourglass) which consists of a minimum of 10 stars in a 4 arc second radius (= 2 of my pixels). The Hourglass itself is around 15" x 30". This is well-described in the paper [1] whose Figure 1 shows what the region looks like in near-infrared. I read somewhere (but can't lay my hands on it now) that this group of stars is exceedingly young -- 10 thousand years only. Amazing to think that they would have started on their journey at the time we humans were starting to think about building our first cities. Now I need to wait for a few more years to match this seeing.... cheers Martin [1] https://arxiv.org/pdf/astro-ph/0506552.pdf

Thanks Chris for that link. Here's most of the rest that I observed over 2 nights this week. They consist of 8 of the 11 NGC PNs in Aquila (turns out I didn't manage to get 2 of them in the frame) plus Abell 65 which lived up to its billing as faint... These are mainly 4 or 5m total exposures with around a minute of each of RGB. They are all at the same scale. The ones that are not obvious are Abell 65 (a blue-grey oval smudge a little larger than NGC 6781 below it), NGC 6741 (the pink coloured object) and NGC 6803 (the green-blue oval just above centre). This latter was near the edge of the frame and although it is supposedly elliptical it isn't quite as elliptical as that... Data laid out as in image mag SB cstar diam mag SB cstar diam mag SB cstar. diam 6778 AQL 12.1 20.0 16.9 0.26' 6804 AQL 12.2 22.5 14.4 0.58' Abell 65 SGR 13.8 22.7 15.9 1.7' 6751 AQL. 11.5 19.4 15.4 0.34' 6852 AQL. 12.9 21.4 17.9 0.47' 6781 AQL 11.8 23.2 16.8 1.8' 6741 AQL 11.4 17.1 20.3 0.13' 6807 AQL 12.2 14.9 16.3 0.03' 6803 AQL 11.3 16.2 15.2 0.09' The central stars are visible in some of these. NGC 6804 is stubbornly grey no matter how much I push up the saturation. The surface brightness doesn't correspond too well to my impressions here, esp. for NGC 6781. Some are crazily small and bright. I'd like to revisit these in narrowband at some point. To see how small these are, here is the full frame version of NGC 6781 on the tiny Lodestar sensor. cheers Martin

Another reason colour helps is because the transmissivity is so much lower. With some PNs I've had more success with linear 'stretch' ie no stretch. I've a feeling we need an anti-stretch. Once I've observed a reasonable number I'm going to see if I can see a pattern to success/failure.

All images are welcome, especially single frames like this. Thanks for posting! It must have been a great to see the planetary appear in the frame. What is the NGC designation of the Blue Snowball? Apparently, the second one I posted is known as the Little Gem.... but to me, that is a name I can only associate with those tiny biscuits with a colourful dollop of icing sugar I used to eat as a kid! Martin

From the same session, this is NGC 6445, a mag 13.2 PN, also in Sagittarius, this time with a surface brightness of 22.0. This 'wide' field shot shows the object, just over half an arc-minute in diameter, sitting in a somewhat less crowded star field. (This is one minute in RGB (4 x 15s subs) plus a few minutes of 5s luminosity subs.) It is described in one abstract as "a non-symmetric type I bipolar nebula with a very bright central ring, opened lobes, and remarkable features." Some of the structure can be seen in a single 5s sub but the addition of colour shows further features. The right hand edge seems more diffuse/wispy than the left. I'm seeing this as a tilted hourglass, presumably the pair of lobes spreading out from a pinched central region. The central star has magnitude 19.0. Consulting the figures in this paper I see that in fact all I have caught is the 'very bright central ring'. The lobes are barely visible in broadband imaging. The lobes in the images from the article are visible to differing extents in H-alpha, O-III and S-II. This is definitely one to return to with narrowband to try to catch some of the butterfly-like wing structures (seen in H-alpha) that would be visible to the upper left and lower right. These extend more than 1 arc-minute to each side. The left panel is my shot inverted and heavily stretched, compared to the H-alpha panel from the above paper. Cheers Martin